On a Unisystem, only the SW2 side gets populated. The Dualsystem (both Red Tent and Dual Upright) you can populate both sides of the board and the 2 games will play on opposite screens. If you have Balloon Fight, Wrecking Crew, Baseball, or Tennis, these games use 12 eproms, that populate the borad. These are the only head-to-head games, in the Vs library. This is why your eproms are labeled 1A or 6A etc. It refers to the placement on the board.